1. Field
Apparatuses and methods consistent with exemplary embodiments relate to decrypting a ciphertext into a plaintext, and more particularly to improving security of a secret key when performing encryption and decryption of a plaintext.
2. Description of the Related Art
A system including apparatuses which communicate with each other, for example, a server and a client, is widely used in various fields of electronic and communication technologies. For example, in an image processing system, a content providing apparatus that is a server transmits content such as image-data to a content playback device that is a client through a wire-based and/or wireless network, and the content playback device processes and presents the image data as images.
However, as various service models providing content are developed, attacks have been often launched to leak data to an unauthorized third person while transmitting the data. For example, in a communication environment, there could be an interception of data while the data is transmitted from a server to a client, or malicious programs could be embedded in a client to decode a data code.
Thus, data cryptography has been suggested in order to prevent illegal access to content and to protect the copyright on content. For example, a black-box cryptography uses a cryptographic algorithm embedded in separate hardware which an attacker cannot identify. However, the black-box cryptography may involve costs of hardware use, installation issues, difficulty of updating/patch when internal defects occur, etc. On the other hand, a white-box cryptography employs software for protecting a secret key.
However, when an attack happens on a client by memory dumb, the white-box cryptography may allow data to be decoded through the analysis of codes in the memory. Thus, in white-box cryptography, the data needs to be encrypted in a way that it cannot to be decoded by a white-box attack.